Not only are the fields different size, but the COMP field is basically useless. The value contained would neither be the original input nor the desired COMP value.

Suggest you change your expectation. . .

At the top of the page is a link to "IBM Manuals". At the top of the list are some COBOL Language Reference manuals. Look in the manual for your version of COBOL for information about numeric fields. If you find something in the manual that is not clear, post what you found and your doubt about it.

Ah Dick, cut him/her a break.....
Your redefine is only redefining the first four bytes of the nine byte field, if that is what you want, ignore the compile warning....
Since the length is nine bytes, you have a problem....
As far as I know the max comp field is 9(18) which is eight bytes (more commonly known as a double word).
What do you expect to do with the extra trailing byte?